Er-doped hybrid waveguide amplifiers with multiple spatially engineered active layers for on-chip optical gain enhancement

Over the last decades, rare-earth-doped materials such erbium, holmium and thulium have been extensively studied as a cost-efficient solution for optical amplification and lasing on the silicon photonic platform. When combined with suitable host medium and integrated circuit design, rare-earth doped materials can be tailored into efficient and low-noise integrated devices such as waveguide amplifiers and lasers with relatively straightforward and cheap fabrication techniques. Despite their superior properties and potential, rare-earth-doped waveguide technology still remains relatively immature when it comes to the production of competitive building blocks for the silicon photonics industry. Further improvements, such as higher gain, scalable fabrication process and lower deposition temperatures need to be pursued for ultimate cost-efficiency and silicon photonic circuit compatibility. In this work, we present a novel waveguide amplifier design that combines silicon nitride strip waveguides and multiple spatially engineered erbium-doped active layers to improve the gain characteristics of hybrid waveguide amplifiers fabricated on silicon with cost-effective and mass-scalable methods. By spatially controlling the erbium-ion distribution of the proposed multilayer waveguide amplifier such that it matches the transverse intensity distribution of the fundamental mode propagating within the device, we show up to 30% enhanced optical gain when compared to an amplifier design that utilizes only a single gain layer. The design, enabled by atomic layer deposition, opens a completely new approach in developing silicon-integrated waveguide amplifiers and lasers with as high efficiency extracted from the active section as possible.